In the field of blood collection and separation, there has been no device which provides in one integrated article, the necessary components to first collect the blood, second do a phase separation to isolate plasma or serum, and third to dispense the serum. Instead, typically what has been done is, a syringe (device 1) collects the blood in a phlebotomy tube. This tube is then removed from the syringe, and either taken to a centrifuge, or poured off into a tube (device 2) to be spun in a centrifuge to achieve serum separation. Thereafter, the separated serum is then transferred to a container (device 3) that will allow dispensing of selected fractions of the serum.
More recently, device nos. 2 and 3 noted above have been combined into one device, as shown, for example, in U.S. Pat. No. 4,012,325. However, even that device and others like it did not totally integrate into it the blood collection phase--that is, a separate syringe still was required to collect the blood in a venipuncture step, and to transfer the blood to the device.
Yet another drawback with prior devices has been the inability to collect and dispense small amounts of serum from the same device that collects the whole blood. Although some devices have been described that do provide for serum separation and dispensing, generally these have been for fairly large amounts. Although the volume that is transferred in the device of U.S. Pat. No. 4,136,036 is only about 150 .mu.l, such a device is useful only for skin puncture. Further, because a gel displacement method is used to decant the serum, large g forces (&gt;2000 g's) are typically required, and many minutes (&gt;10 min.), making such a device inconvenient for STAT medical situations. Still further, since a maximum quantity of 75 .mu.l of serum is transferred to the larger volume dispensing devices, much of the volume of the serum stays on the large surface area of the large dispenser and thus is unavailable for dispensing. Yet, if the dispenser volume is decreased, there is a higher risk that air entrapment will occur when the serum is transferred to the smaller volume of the dispenser because of the uncontrollable nature of surface wetting. In this situation, dispensing would form air and liquid droplets, resulting in imprecise liquid dispensing.
Therefore, there has been a need prior to this invention to a) integrate all the functions of blood collection, separation and dispensing into a single article of manufacture so that whole blood from a vein enters one end, and serum is dispensed from another end, and b) to do this in a manner that permits smaller amounts of serum to be collected.